The present invention generally relates to removable storage devices for electronic information. More particular, the present invention relates to compensating for data sector timing variations due to drive eccentricity.
Consumer electronics including television sets, personal computers, and stereo or audio systems, have changed dramatically since their availability. Television was originally used as a stand alone unit in the early 1900's, but has now been integrated with audio equipment to provide video with high quality sound in stereo. For instance, a television set can have a high quality display coupled to an audio system with stereo or even "surround sound" or the like. This integration of television and audio equipment provides a user with a high quality video display for an action movie such as STARWARS.TM. with "life-like" sound from the high quality stereo or surround sound system. Accordingly, the clash between Luke Skywalker and Darth Vader can now be seen as well as heard in surround sound on your own home entertainment center. In the mid-1990's, computer-like functions became available on a conventional television set. Companies such as WebTV of California provide what is commonly termed as "Internet" access to a television set. The Internet is a world wide network of computers, which can now be accessed through a conventional television set at a user location. Numerous displays or "wet sites" exist on the Internet for viewing and even ordering goods and services at the convenience of home, where the act of indexing through websites is known as "surfing" the web. Accordingly, users of WebTV can surf the Internet or web using a home entertainment center.
As merely an example, FIG. 1 illustrates a conventional audio and video configuration, commonly termed a home entertainment system, which can have Internet access. FIG. 1 is generally a typical home entertainment system, which includes a video display 10 (e.g., television set), an audio output 20, an audio processor 30, a video display processor 40, and a plurality of audio or video data sources 50. Consumers have often been eager to store and play back pre-recorded audio (e.g., songs, music) or video using a home entertainment system. Most recently, consumers would like to also store and retrieve information, commonly termed computer data, downloaded from the Internet.
Music or audio have been traditionally recorded on many types of systems using different types of media to provide audio signals to home entertainment systems. For example, these audio systems include a reel to reel system 140, using magnetic recording tape, an eight track player 120, which uses eight track tapes, a phonograph 130, which uses LP vinyl records, and an audio cassette recorder 110, which relies upon audio cassettes. Optical storage media also have been recognized as providing convenient and high quality audio play-back of music, for example. Optical storage media exclusively for sound include a digital audio tape 90 and a compact disk 10. Unfortunately, these audio systems generally do not have enough memory or capacity to store both video and audio to store movies or the like. Tapes also have not generally been used to efficiently store and retrieve information from a personal computer since tapes are extremely slow and cumbersome.
Audio and video have been recorded together for movies using a video tape or video cassette recorder, which relies upon tapes stored on cassettes. Video cassettes can be found at the local Blockbuster.TM. store, which often have numerous different movies to be viewed and enjoyed by the user. Unfortunately, these tapes are often too slow and clumsy to store and easily retrieve computer information from a personal computer. Additional video and audio media include a laser disk 70 and a digital video disk 60, which also suffer from being read only, and cannot be easily used to record a video at the user site. Furthermore, standards for a digital video disk have not been established of the filing date of this patent application and do not seem to be readily establishable in the future.
From the above, it is desirable to have a storage media that can be used for all types of information such as audio, video, and digital data, which have features such as a high storage capacity, expandability, and quick access capabilities.
Reading and writing to magnetic disks within removable cartridges provide unique challenges not fully appreciated or addressed by fixed disk drive units. For example, the magnetic disks within removable cartridges are typically subject to greater temperature, humidity, particulate contamination, shock, mechanical stresses, etc. than magnetic disks that are sealed and protected inside fixed disk drive environments. Further, removable cartridges are repeatedly inserted and ejected from removable drive units, whereas fixed disk drives are not. As a result, removable drive units receiving such removable cartridges must be able to adapt to the greatly varying conditions of the magnetic disks.
FIG. 7 illustrates one particular difficult problem not faced by fixed disk drive units is that the variation in eccentricity between different magnetic disks. FIG. 7 includes a magnetic disk 900 having a cylinder 910. The geometric axis of rotation 920 of magnetic disk 900 is shown, as well as an eccentric axis of rotation 930.
Drive eccentricity typically refers to the variation in the axis of rotation for a magnetic disks. Typically magnetic disks are rotated around geometric axis of rotation 920 and preformatted in the factory with well known servo bursts at regularly spaced intervals, for example along cylinder 910.
FIG. 8 illustrates an ideal timing diagram of signals from a magnetic disk. FIG. 8 includes a servo burst signal 1000 and a data sector signal 1010. Servo burst signal 1000 includes servo bursts 1020-1050, and data sector signal 1010 includes data sectors 1060-1110. As illustrated, the nominal latency x between servo burst 1020 and data sector 1060 is the same as between servo burst 1040 and data sector 1090, and the nominal latency y between servo burst 1030 and data sector 1080 is the same as between servo burst 1050 and data sector 1110. Further the nominal timing t between servo bursts 1020, 1030, 1040, etc. respectively is the same.
In this example, data sectors 1070 and 1100 are split between two servo sectors, thus preferably servo burst 1020 is used for accessing data sectors 1060 and 1070, servo burst 1030 is used for accessing data sector 1080, servo burst 1040 is used to access data sectors 1090 and 1100, and servo burst 1050 is used to access data sector 1100.
FIG. 9 illustrates a typical timing diagram of signals from an eccentric magnetic disk. FIG. 9 includes a servo burst signal 1000' and a data sector signal 1010'. Servo/burst signal 1000' includes servo bursts 1020'-1050', and data sector signal 1010' include data sectors 1060'-1110'. As illustrated, the actual latency between servo burst 1020' and data sector 1060' is "x+x1", 1120', the actual latency between servo burst 1030' and data sector 1080' is "y+x2", 1121', the latency between servo burst 1040' and data sector 1090' is "x+x3", 1122', and the latency between servo burst 1050' and data sector 1100' is "y+x4", 1123'. In this case x1 and x2 are positive, and x3 and x4 are negative. Further the actual timing between servo bursts 1020' and 1030' is "t+t1", 1130', the time between servo bursts 1030' and 1040' is "t+t2", 1131', the time between servo bursts 1040' and 1050' is "t+t3", 1132', and the time between servo bursts 1050' and the next servo burst is "t+t4", 1133'. In this case t1 and t2 are positive and t3 and t4 are negative.
FIG. 9 illustrates the effect of drive eccentricity upon the timing of servo burst signals and data sector signals. As illustrated, the timing between servo bursts can increase from the nominal timing "t" 1130 to the actual timing "t+t1", 1130' or decrease to the actual timing "t+t3", 1132'. At the same time the latency between servo bursts to the next respective data sectors can increase from the nominal latency "x", 1120 to an actual latency "x+x1", 1120' or decrease to an actual latency "x+x3", 1122'.
FIG. 10 illustrates a typical "padding" solution for addressing drive eccentricity with reference to FIG. 9. Previously, if it were determined that the worse case (maximum) latency between a servo burst and the next data sector was "x+x1" 1120', this additional latency deviation "x1" was then added to nominal latencies for subsequent data sectors, regardless of the actual latency. For example "x+x1" would be applied as the latencies between servo bursts 1020', 1030', 1040', etc. and when the next data sector could be read.
In the example in FIG. 10, after servo burst 1020' the next data sector can be read after a "x+x1" latency is data sector 1060'. However, after servo burst 1030' the next data sector can be read after a "y+x1" latency; in this case data sector 1090', not 1080'. Further, after servo burst 1040' the next data sector that can be read after a "x+x1" latency is data sector 1100', not data sector 1090'.
In FIG. 8, data sector 1090 was referenced with respect to servo burst 1040; however, when the padding solution is used, in FIG. 10, data sector 1090' can only be referenced with respect to servo burst 1030'. As a result, if the MR head were currently at location 1140', in order to access data sector 1090', the magnetic disk would have to make more than one complete revolution before data sector 1090' could be accessed. This substantial delay is a drawback with this padding solution.
Thus, what is needed is a method and apparatus for allowing enhanced accessing of eccentric magnetic disks within removable cartridges.